1. Field of the Invention
The present invention relates to an electromobile (electric car) in which an internal combustion engine is replaced by an electric motor to reduce noises and eliminate emission of the engine exhaust gases.
2. Description of the Prior Art
The electromobile is run by the output torque produced by an electric motor to which a motor current is fed from a battery.
In a brushless motor composed of a rotor made of a permanent magnet and a stator coil, three-phase sinusoidal waves are generated corresponding to the-positions of the magnetic poles of the rotor. A current command is superposed on the sinusoidal waves by a motor controller to produce a PWM signal, which is converted into a sinusoidal phase current, i.e. a motor current, by an inverter circuit and is fed to the motor.
FIG. 2 is a block diagram showing an electromobile of the prior art. In FIG. 2 reference numeral 21 designates a shift switch for detecting the range position selected by the driver's manipulation of a shift lever (not-shown), i.e. the position of the shift lever. Numeral 22 represents a CPU equipped with RAM, ROM and the like for controlling the electromobile in its entirety; numeral 23 a motor controller for producing three-phase sinusoidal waves corresponding to the magnetic pole positions of the rotor to produce the PWM signal by superposing a current command upon the sinusoidal waves; and numeral 24 an inverter circuit composed of a plurality of power transistors for converting the PWM signal produced by the motor controller 23 into a motor current having the sinusoidal waves and fed to a motor 25. Numeral 26 designates a battery.
In the electromobile thus constructed, the output torque of the motor 25 is controlled by changing the current command also referred to as the output torque command. Moreover, the motor current is fed back to match the current command.
If neutral (N) or parking (P) is selected in the electromobile of this kind, the CPU 22 outputs a torque command to set the output torque to O.
In the electromobile in which the wheel axle and the motor 25 are directly connected, there is no means for disconnecting the axle from the motor 25. Thus, it is decided by the CPU 22 whether or not the drive wheels are to be rotated.
FIG. 3 is a schematic diagram showing an electromobile of the prior art, in which the axle and the motor are directly connected. In FIG. 3 reference numeral 21 designates a shift switch; numeral 22 a CPU numeral 23 a motor controller; numeral 24 an inverter circuit (INV); numeral 25 a motor; and numeral 27 drive wheels. The inverter circuit 24 converts the PWM signal produced by the motor controller 23 into the motor current and feeds the motor current to the motor 25. In this case, the CPU 22 outputs the drive signal to the inverter circuit 24 so that the motor 25 is energized to drive the drive wheels 27 when the drive signal is ON.
In the electromobile of the prior art described above, however, the CPU 22 calculates the output torque command and produces the drive signal. In case of a malfunction in the motor controller 23, in the switching elements of the inverter circuit 4 or in the CPU 22, therefore, it may be impossible to sufficiently control the motor current fed to the motor 25 or to set the output torque command to O.